Light valve



J. R LONG LIGHT VALVE March 15, 1938.

Filed Oct. 14, 1935 Patented Mar. 15, 1938 UNITED STATES PATENT OFFICE Claims.

This invention relates to light valves, that is, devices for modifying light rays responsive to sound waves for the purpose of producing records of the sound waves which may be used in con- 5 nection with motion pictures.

The invention has many objects (which will be understood by those skilled in the art) among which are the following:

To provide a light valve of simple, light and compact construction;

To provide a light valve having a complete and effective damping system;

To provide a light valve which is very rugged and particularly one whose light shutter is not easily dislodged from the initial position;

To provide a light valve which is capable of producing variable density sound records of a range and clarity surpassing those of the prior art devices;

To provide a light valve in which the objective optical assembly is an integral part of the valve, with a lens of such focal length that the slit is greatly reduced, thus making the slit adjustment less critical; 7

To provide a light valve requiring a minimum amount of power for eflicient operation;

To provide a light valve in which the shutter barely exceeds the length necessary for modulate ing the light beam and whose shutter is actuated directly by the voice coil and magnet;

To provide a light valve which will produce records rich in tonal quality and faithful reproductions of the entire useful audible-range; and

In general, to obviate defects common to known types of light valves and to provide a light valve especially adaptable to portable or traveling recording machines.

In the accompanying drawing forming a part of this specification and showing a preferred embodiment of the invention,-

Fig. 1 is a sectional plan view of the light valve and optical assembly;

Fig. 2 is an end view of the light valve;

Fig. 3 is an enlarged perspective view of details of the light valve;

Fig. 4 is an elevation of the preferred device for stretching the armature to increase its period of resonance; and

Fig. 5 is an end view of the armature after it has been stretched.

Referring particularly to the drawing. and first to Figs. 1 and 2, there is shown a light valve 5 assembled with a lens casing 6, said lens casing having a reduced end I through which a beam of light may emerge, and a lens (not shown) for focusing the light beam on a slit provided in the light valve as will be described.

As the lens casing 6 is of standard construction, except for its connection to make an assembled unit with the novel light valve of the 5 invention, its interior construction is not illustrated. A collar 8 provides a union between the lens casing and the light valve 5 and a screw 9 permits disassembly of these parts.

The light valve 5 comprises a hollow cylindrical 10 body, as shown, whose axis coincides with the longitudinal axis of the casing 6. An armature III, which is a thin plate of any suitable material, for example metal, extends across the body of the valve at a slight angle to a diametric plane, and is 15 carried in rubber cushions II which embrace the armature at two opposite corners, said cushions H being fixed in diametrically opposite slots I2 cut in the valve body. A pole piece i3 is secured to the valve body and lies at right angles to its axis. 20 A magnetic coil 14 is wrapped about the pole piece and is connected to a wire l5 leading to the recording amplifier previously mentioned.

Directly above the armature and in the same plane with the pole piece [3 is fixed blade l6 whose 25 inner beveled edge almost touches the armature, the latter thus being free to vibrate between the opposed edges of the pole piece and the blade. A slit or narrow gap is formed by the relative positions of the pole piece and blade, and the arma- 30 ture as it vibrates will obviously vary the slit and hence affect any beam of light passing through said slit. A permanent horseshoe magnet 11 is pivotally attached at one of its poles by a bolt i8 to the pole piece l3. A light guard I9 is at- 35 tached to the valve body and has a fiat plate I So with a curled edge l9b which prevents the light from passing through the light valve anywhere except through the said gap.

In operation, the incoming current from the re- 40 cording amplifier travels through wire l5 and coil it, thus magnetizing the pole piece l3, which is in the field of permanent magnet I1. The changes in magnetization of the pole piece l3 cause the armature ill to vibrate, thus changing 45 the width of the slit between the armature and the blade I6. As the slit is varied, the character of the light beam passing through it is varied, thus varying the light image recorded by the photographic film which is back of the light valve. 50 It will be understood that the slit is adjusted by the manufacturers of the device and that no adjustment of any kind can be made by a user.

It has been found that the employment of the rubber cushions H to dampen the armature is 55 a very important improvement, since it results in recordings of a high fidelity to the original sound impulses. Also, the use of a magnet ill, especially if adjustable as shown, results in superior recordll'lgS- Fig. l shows the armature it between two collars El, 22, collar 2i being fixed to the valve housing and having re-entrant ends or edges 2 lla adapted to receive the beveled ends or edges 22a, of adjustable collar 22. A member (not shown) interposed between collar 22 and the housing, will move the ends 22a towards the collar ends Zia, clamping the ends of the armature l and causing the armature to assume the shape shown in Fig. 5. Thus the armature is stretched and its natural period of resonance is raised. This has been found extremely desirable for perfect operation of the valve.

Among the advantages of the described light valve are the following:

(a) It is easily portable and is highly serviceable because it is of a rugged construction;

(b) It has a wide frequency response;

(0) It is inexpensive;

(d) It saves batteries;

(e) It is less expensive to operate than any known recording unit;

(1) Its recording density is constant.

The present invention attains all the objects and desiderata mentioned above, as well as others not mentioned, and obviously may be embodied in several forms neither shown nor described.

Having described a preferred embodiment of the invention, what I claim as new and desire to secure by Letters Patent is.-

1. A light valve comprising, in combination, a body which is hollow and cylindrical; diametrically opposite slots cut in said body from one end, said slots extending in a plane at a slight angle to the longitudinal axis of the body; an armature consisting of a thin rectangular plate two of whose corners are within the two slots; rubber cushions embracing said corners and tightly fitting the slots and providing mount ing means for said armature; means providing amines a sht for free edge of sa dv armature; and electi e-ma i tie including a. pole piece, for efi'ecting vibration of said armature.

2. In a light valve, a resilient metal plate member, means securing the plate by its ends to have its plane inclined to a. beam of light traversing the valve to have an upper edge of the memmr form the edge of an exposure slit, and electromagnetic means responsive to sound signal currents for oscillating said edge in accordance with fluctuations of said signal currents to affect the opening of said slit accordingly.

3. In a light valve having a variable exposure slit through which a beam of light is passed, a

length of resilient metal inclined at an angle to the beam path to form a boundary line of said slit, the metal being in a relatively fixed position and means adjacent each end of the slit effecting said fixed position and leaving the central portion of the metal free to vibrate and electro-magnetic means adjacent said metal for setting up vibrations therein, the field of said means being directed to cause said metal to tend to vibrate in planes parallel to said beam path.

4. A light valve comprising a body, a thin ribbon resilient metal member across the body and over which a beam of light is directed, members gripping the metal member on each side of the beam path stretching and positioning the metal member in a plane inclined to said beam, and electro-magnetic means for vibrating said metal member between said gripping members.

5. A light valve comprising a body, a relatively fixed member determining one edge of an exposure slit, a ribbon of thin resilient metal'stretched across the body adjacent said member to define an opposing edge of said slit, means for gripping the metal on each side of said slit, said metal being turned across the slit to have its plane inclined to a beam of light directed through the slit, and electro-magnetic means for vibrating the slit bounding portion of the metal to efiect variations in the slit opening.

JOHN ROBERT LONG. 

